The present invention relates to a color image recording apparatus for exposing a photosensitive recording medium through mask members, and more particularly to a color image recording apparatus having a registering mechanism for registering mask members.
There is known as color image recording apparatus in which mask members or intermediate sheets corresponding to three primaries are produced by a monochromatic printer and electrostatically carried by a feed belt into an exposure unit in which a color latent image is formed on a photosensitive recording medium by exposure through the mask members. It is highly important that the mask members on the feed belt be accurately registered in the exposure unit in order to expose the photosensitive recording medium to three primary images which are superposed precisely for thereby producing a colored image of high quality. Therefore, there has been a demand for a registering mechanism for registering the mask members with high accuracy.
The applicant has proposed an apparatus employing a novel registering mechanism for superposing three primary images precisely on a photosensitive recording medium and exposing the photosensitive recording medium to the three primary images, as disclosed in U.S. patent application Ser. No. 07/255,342.
The disclosed apparatus comprises, in the gap between a light source and a photosensitive recording medium, a belt drive means for carrying and feeding mask members on a feed belt, two belt support moving means, i.e., front and rear end belt support moving means, for moving a belt support which supports the feed belt in a direction substantially normal to the direction in which the feed belt feed the mask members, and positioning sensors disposed in confronting relation to the feed belt, the positioning sensors serving to read positioning reference marks on each of the mask members.
Each of the mask members is fed by the feed belt to a position very close to the position where the photosensitive recording medium will be exposed, and then the positioning reference marks (which have been formed at the same time as the mask image) on the mask member are read by the positioning sensors. Based on signals from the positioning sensors, the belt drive means and the two belt support moving means are controlled by a control means so that any inclination or skew of the mask member with respect to the feeding direction and positional displacements of the mask member in the feeding direction and the direction normal thereto will be eliminated.
By employing the positioning reference marks on each of the mask members and the belt drive means and the two belt support moving means, which serve as a position correcting means, the three mask members can be registered more accurately and as a result the three primary images can be superposed more precisely for exposure, than a conventional positioning arrangement in which the mask members are positionally corrected by only a belt drive means through the detection of the leading edges of the mask members.
However, the control of operation of the feed belt which is used for registering the mask members in the earlier apparatus cannot be speeded up and is relatively inaccurate. More specifically, the stroke of each incremental step of a stepping motor which actuates the feed belt remains the same while the mask members are being fed and subsequently registered. Accordingly, if the stroke of each incremental step of the stepping motor is increased to speed up the feeding of the mask members, then the accuracy with which the mask members are registered is lowered. Conversely, if the stroke of each incremental step is reduced to achieve greater registering accuracy, then the speed at which the mask members are fed is lowered.
In the disclosed apparatus, the completion of a registering process is confirmed by determining whether the output signal from each of the positioning sensors has exceeded a threshold level or not. This arrangement cannot directly determine whether a mask member is positioned in a target position or not, i.e., it can determine only whether a mask member has moved past the target position or is still positioned before the target position. In order to stop a mask position exactly in the target position, a highly precise control procedure for de-energizing the belt drive means the instant the output signal from the positioning sensor exceeds the threshold level must be employed.
After a mask member has been registered in the feeding direction, for example, according to one of the positioning sensors, the mask member is corrected out of any skewed condition with respect to the feeding direction according to another positioning sensor. At this time, the mask member may be positionally displaced again in the feeding direction by being corrected out of the skewed condition. Such a positional displacement can on longer be detected if it occurs past the target position since, as described above, the positioning sensors can determine only whether a mask member has moved past the target position or is still positioned before the target position.
Therefore, each time a mask member is positionally corrected in the feeding direction or the direction normal thereto, or out of any skewed condition according to one of the positioning sensors, the mask member that has been corrected in the other directions has to be fed back and registered again in those other directions according to the other corresponding positioning sensors. Consequently, the entire process of completely correcting the mask members in all the directions is time-consuming.
The mask member registering process is composed of the step of correcting the position of a mask member in the feeding direction, the step of correcting the mask member out of e skewed condition, and the step of correcting the position of the mask member in the direction normal to the feeding direction. These correcting steps are successively carried out at different times As a result, it is time consuming to finish the entire registering process.